Biomedical Engineering Reference
In-Depth Information
(a)
System
correction
System
correction (4x)
4 × 4 independent,
reconstruction
4 × 4 independent,
measured phase
4 × 4 w/ 2 × 2 overlap,
reconstruction
4 × 4 w/ 3 × 3 overlap,
reconstruction
lateral
19,000
14,250
9,500
4,750
0
axial
4 × 4 independent,
reconstruction
4 × 4 independent,
measured phase
4 × 4 w/ 2 × 2 stepped overlap,
reconstruction
4 × 4 w/ 3 × 3 stepped overlap,
reconstruction
(b)
2
2
2
1
1
1
1
0
0
0
0
FIGuRE 13.15 AO.correction.on.a.1-μm-diameter.bead.under.a.250.μm.ixed.brain.slice,.using.diferent.varia-
tions.of.our.pupil.segmentation.algorithm..(a).Lateral.and.axial.images.of.the.bead.obtained.with.(let.to.right):.sys-
tem.aberration.correction.only;.system.aberration.correction.with.4.×.display.gain;.4.×.4.independent.subregions.
with.reconstructed.phase;.4.×.4.independent.subregions.with.measured.phase;.4.×.4.stepped.overlap.with.2.× 2.
steps.and.phase.reconstruction;.and.4.×.4.stepped.overlap.with.3.×.3.steps.and.phase.reconstruction..Scale.bars:.
2.μm..(b).Final.corrective.wavefronts.in.units.of.excitation.light.wavelength.(850.nm).ater.subtraction.of.system.
aberrations..(Ji,.N.,.et.al.,. Nat. Meth .,.7,.2,.141-147,.2010.)
13.5.3 Field Dependence and Averaged correction
A.two-photon.luorescence.image.is.acquired.by.scanning.the.laser.focus.across.the.desired.ield.of.
view. ( Figure. 13.16 ) .. During. the. scan,. the. excitation. light. travels. through. diferent. tissue. environ-
ments. and. thus. experiences. diferent. aberrations.. If. the. luorescent. feature. used. to. measure. image.
shit.during.AO.is.spatially.extended.(e.g., . Figure.13.16a ),.the.resulting.correction.will.relect.an.aver-
aged.aberration.across.the.image.ield,.rather.than.a.more.local.correction,.as.would.be.the.case.if.the.
corrective.feature.were.point-like.(e.g., . Figure.13.16b ) ..Certain.applications.may.require.a.locally.opti-
mized.correction,.while.for.others,.an.averaged.correction.may.be.more.desirable,.especially.when.a.
large.ield.of.view.is.covered.during.imaging.(e.g.,.calcium.imaging.of.a.population.of.neurons)..For.
both. single-segment. illumination. and. full-pupil. illumination. methods,. one. can. obtain. AO. correc-
tions.applicable.either.locally.or.over.a.broad.area.by.choosing.diferent-sized.sample.features.during.
measurement.
 
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